Treatment of controlled discharge leachate by coagulation-flocculation: influence of operational conditions

Abstract

ABSTRACT The aim of this study was to optimize the operational conditions of the coagulation-flocculation process for the clarification of leachate from the landfill Technical Center of Souk-Ahras city. Three coagulants (ferric chloride, aluminum sulfate and ordinary alum) were tested and two types of agitation (mechanical and ultrasound) were implemented. The quality of treatment was assessed via physicochemical and bacteriological analyzes. The parametric study revealed that pH adjustment of leachate was crucial for the success of treatment. The stronger reduction of turbidity was obtained with a coagulant dose of 15%, a stirring speed of 250 rpm and a stirring time of about 5 min for both aluminum sulfate and ordinary alum and 15 min for ferric chloride. An optimum coagulant-to-leachate volume ratio of one was found for the three coagulants, resulting in a turbidity reduction of 99.4%, 98.9% and 98.6% with ferric chloride, aluminum sulfate and ordinary alum, respectively. Bacteriological analyzes highlighted the absence of total germs, fecal coliforms and streptococci for leachates treated with ferric chloride or aluminum sulfate. In contrast, coliforms including 9 total germs, 4 fecal germs and 3 fecal streptococci per 100 mL were detected for leachates treated with ordinary alum. The treatment of leachate was improved by using ultrasound waves with a frequency of 37 kHz and a power of 30 W. Indeed, a significant decrease in the turbidity of supernatants was observed as compared with the use of mechanical agitation, and a value of 0.19 NTU (instead of 0.61 NTU with mechanical agitation) was obtained for a treatment carried out with ferric chloride. The clarification of leachates was optimal at 20°C providing a BOD5 of 100 mg O2/L for both ferric chloride and aluminum sulfate, and 200 mg O2/L for ordinary alum.